In view of increasing oil prices and declining reserves, the demand for increased recovery and production of oil from oilfield reservoirs has been growing. Traditional oil production processes, often referred to as primary and secondary recovery, may only be capable of recovering 20-40% of the reserves in an oilfield reservoir. As such, a demand has arisen for more advanced processes capable of extracting additional reserves from existing oilfield reservoirs.
The term Enhanced Oil Recovery (EOR) is used in connection with a number of different recovery techniques capable of recovering additional reserves from oilfield reservoirs. In many instances, EOR techniques may be used to recover 25% or more of the remaining reserves in an oilfield reservoir. EOR techniques may include a wide variety of different technologies, such as some forms of waterflooding, gasflooding (e.g., using hydrocarbon gas, nitrogen and/or carbon dioxide), chemical flooding (e.g., using polymers, surfactants and/or alkalis) and thermal techniques (e.g., steam injection, hot water injection, electrical heating and/or combustion), among others.
However, selection of the optimal EOR technique, or combination of EOR techniques, for a particular oilfield reservoir is highly dependent upon the properties of the reservoir (e.g., temperature, pressure, salinity, oil composition, rock properties, etc.) as well as additional concerns such as economic factors (e.g., up front capital investment, current and/or projected oil prices, ongoing implementation costs, etc.) One technique that may provide superior results for one oilfield reservoir (generally represented by a metric such as Incremental Recovery Factor (IRF)) may be too costly, or may provide sub-optimal results, for another oilfield reservoir. However, the selection of a particular EOR process (hereinafter, either an EOR process or an EOR scheme), associated with a particular level of recovery from an oilfield reservoir, traditionally has been accomplished in a time consuming and disintegrated manner, and based upon substantial human knowledge and expertise.
More recently, software-based tools have been developed to automate and otherwise facilitate the selection of EOR processes and generate estimations of incremental recovery that may be expected from EOR processes for a given oilfield reservoir. One limitation of such software-based tools, however, has been that such tools are limited to single porosity systems and models, i.e., non-fractured reservoirs where the porosity of the reservoir may be adequately represented by the porosity associated with the rock matrix of the reservoir.
Existing software-based tools, however, are incapable of analyzing EOR processes for other types of oilfield reservoirs, and in particular multiple-porosity systems such as naturally-fractured reservoirs (NFR's) where the porosity of the reservoir is based upon not only the porosity of the rock matrix but also the porosity of fractures in the rock matrix. It has been found, in particular, that flow and recovery systems as well as the rock heterogeneity are substantially more complex in NFR's than in non-fractured reservoirs, and as a result, existing software-based tools are generally incapable of generating sufficiently accurate estimations of incremental recovery.
Therefore, a substantial need continues to exist in the art for an improved manner of facilitating the selection of EOR processes and estimating incremental recovery from such processes for naturally-fractured reservoirs.